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Screws Index Page...

Wrench / spanner clearances around screw Heads . ...

Important Note

The information below is generally based on conservative appraisals of the clearance required for open ended spanners, ring spanners, and sockets. It is probable that smaller dimensions can be used if the wrench / spanner / socket geometry is selected at the early design stage.    The links on this table provide more detailed information.

For Bolt edge distances applicable to structural design refer to Edge Distances

Bolts Holes, Min Spacings, and Wrench / Spanner Clearances Precision Hexagon Bolts And Screws

Dimensions in mm

Tables for bolts and screws in accordance with BS 3692:2001..ISO metric precision hexagon bolts, screws and nuts. Specification.

Note clearance hole dimension "D" is in line with BS EN 20273:1992, ISO 273:1979. med fit

Size Hole D Min P Clearance G S
Nom. Size
Spanner(A/F)		 H
(Sq.Drive)
a b c
M3 3.4 14 10 8 10 - 5.5 14(6,3)
M4 4.5 17 10 8 12 14 7 22(10)
M5 5.5 20 10 8 12 14 8 22(10)
M6 6.6 24 14 10 15 17 10 26(12,5)
M8 9.0 30 18 12 18 22 13 26(12,5)
M10 11.0 37 28 14 21 27 17 27(12,5)
M12 13.5 42 30 16 22 30 19 29(12,5)
M16 17.5 50 30 20 26 38 24 42(20)
M20 22,0 60 32 22 32 46 30 47(20)
M24 26,0 75 48 25 38 55 36 54(20)
M30 33.0 94 60 30 48 70 46 70(25)
M36 39.0 104 60 34 52 90 55 81(25)




High Strength Friction Grip Bolts

Dimensions in mm

Clearances suitable for bolts & nuts to BS EN 14399-3:2005.. High-strength structural bolting for preloading. System HR. Hexagon bolt and nut

Size Min P Clearance G S
Nom. Size
Spanner (A/F)
a b c
M16 56 30 25 38 27 27
M20 64 48 28 42 48 32
M24 84 48 40 55 65 41
M30 98 60 45 65 77 50
M36 112 60 45 70 81 60




Relevant links
  1. Tecnocentro Wrench clearances.. Excellent source of relevant information - Better and more detailed than my information
  2. EngineersEdge Wrench Clearances.. American (inch sizes) similar to Information in Machinerys Handbook
  3. Icrank Wrench Clearances.. American (inch sizes) .

Screws Index Page...

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